Michael Ellenbogen says he “felt like a fraud because, for years, I had been in the public eye telling everyone I had Alzheimer’s.” (Courtesy of Michael Ellenbogen)

Twenty years ago, at age 39, I began having memory and cognitive problems. My primary-care doctor and my neurologists said I was stressed and depressed. I also was diagnosed with mild cognitive impairment, or MCI. Ten years later, I received another diagnosis. Well, really two. One doctor said I had Alzheimer’s disease, and another thought it was semantic dementia.

Alzheimer’s is a devastating chronic neurodegenerative disease. It is a progressive mental deterioration that advances to affect bodily functions such as walking and swallowing, and always leads to death. Semantic dementia leads to losses of vocabulary, fluency of speech and meanings of familiar words. It also is progressive.

After another year of testing, physicians decided that I had Alzheimer’s.

While it was a relief to finally get a diagnosis, I realized that I had been given a death sentence. There is no prevention or cure for Alzheimer’s, and no survivors. Overwhelmed, I decided to help the search for a cure by advocating for Alzheimer’s and dementia.

I got involved with clinical trials and advocacy. My huge network on LinkedIn allowed me to connect with advocates and information. It gave me access to many tests, including gene tests, free. Two contacts — health-care professionals — even read my medical records and scans and gave me their opinions.

Alzheimer’s is a complex disease to diagnose. The science is just not there yet. Sixty to 80 percent of dementia cases are said to be due to Alzheimer’s. But postmortem tests of elderly patients have found that dementia has several causes. “Up to one-third are primarily attributable to pathologies” other than [Alzheimer’s disease], primarily cerebrovascular disease and synucleinopathy,” said one study. The latter is a neurodegenerative disease with three types, one of which is Parkinson’s.

Despite my Alzheimer’s diagnosis, I always felt I had other issues — such as losing my temper, a lack of patience and being very reactive to minor issues — that aren’t normally related to Alzheimer’s. As the years wore on and I moved from one clinical trial to another, failing them all, I wondered whether I had been misdiagnosed.

Five years ago, the Food and Drug Administration approved a test called Amyvid, by Avid Radiopharmaceuticals, a subsidiary of Eli Lilly. It is a diagnostic scan that checks for ­beta-amyloid neuritic plaque density in the brain. If sparse to no amyloid plaques are seen on the scan, it is likely that a person does not have Alzheimer’s disease. This test costs about $10,000 and was not covered by insurance. It also was not a definitive test, but one to be used with others to diagnose a cause for cognitive decline.

It took me about two years to get the test. I signed up and was approved for a study by Avid, which was trying to identify subjects for their next clinical trials. I was now 59. It had been two decades since I first raised memory issues with my doctor.

Waiting to learn the results was tough. It takes special expertise to read these scans, and the error rate in reading them was very high. Avid had to send my results to another expert for a second reading, after the first reader had difficulty reading the scan.

Four long weeks later, I got the results. My scan was negative. Was I ever shocked. I also felt like a fraud because, for years, I had been in the public eye telling everyone I had Alzheimer’s.

If I had known this result early on, I never would have wasted all that time in clinical trials for Alzheimer’s. When you are told you are dying, the last thing you want to do is waste time. Not only that, I contributed to the likely failure of those trials because I did not have the amyloid plaques that a particular drug was trying to clear.

Two neurologists have stated that I fall into a fairly new category called suspected non-Alzheimer’s pathophysiology, or SNAP. According to one study, about 23 percent of clinically normal people ages 65 and older and about 25 percent of people with MCI have SNAP. For people with both MCI and SNAP, the risk of cognitive decline and dementia is higher than for clinically normal people with SNAP.

I was initially diagnosed with MCI. But for the past 10 years, the diagnosis has been Alzheimer’s. It is still officially the diagnosis because information gained in trials — which is how I found out that my amyloid scan was negative and that I probably did not have Alzheimer’s — does not go on a medical record.

That reminded me of a friend, an educational scientist who read my medical records about a year ago and insisted I did not have Alzheimer’s. He said I had semantic dementia. So, for now, I will have to accept that I may have either semantic dementia or SNAP.

I will have to wait for science to catch up before I know for sure. Who knows, I may even be part of the next new term. I just hope it means that what I have will not be progressive and lead to death.

The one thing we all should learn from my experience is to take advantage of all the tools we have access to so we can make the best decision possible.

Ellenbogen is the author of “From the Corner Office to Alzheimer’s.”